Processes for treating materials containing nickel and iron



United States Patent PROCESSES FOR TREATING MATERIALS CONTAINING NICKEL AND IRON Edgar B. Mancke, Bethlehem, Pa., assignor to Bethlehem Steel Company, a corporation of Pennsylvania No Drawing. Application December 23, 1953, Serial No. 400,143

4 Claims. (Cl. 75-101) This application is a continuation-in-part of my copending application, Serial No. 274,055, filed February 28, 1952.

My invention is directed primarily to processes for separating nickel and iron in materifls which contain these two elements. My invention is also directed to the treatment of materials containing nickel and iron and which contain other elements such as chromium and cobalt for the purpose of separating these other elements as well as nickel from the iron.

Nickel is associated with iron in many materials. Many ores, for example, contain both of these elements. An object of my invention is to recover nickel from these materials.

An especially important object of my invention is the removal of nickel, or nickel and other non-ferrous metals such as cobalt and chromium, from iron ores to produce an iron product which can be used commercially in the manufacture of iron and steel. While nickel is a valuable constituent of many special steels it is not desirable in any considerable amounts in most of the commercial steels. In large tonnages of steel, in fact, it is usually desired to have the nickel content sufliciently low so that the nickel will have no substantial elfects upon the properties of the steel. It is very important to keep the nickel content of the ore as low as practicable when such ore is to be used in making hot metal or pig iron for the manufacture of steel, in view of the fact that much of the scrap which is used in making steel already contains some nickel. Unless care is taken to use ore which isv low in nickel content when making the hot metal or pig iron the nickel content of the hot metal or pig iron together with the nickel of the scrap can easily cause the nickel content of the finished steel to be'above permissible tolerances.

It is a special object of my invention to remove nickel from iron ores which have hitherto oifered great ditiiculty in treatment to render them available for use in general iron and steel manufacture. An example of such ores are the so-called Mayari type iron ores. In the disclosure of my invention I shall refer to the treatment of Mayari type iron ores for the purpose of setting forth the conditions and principles of the processes which are involved in my invention.

In Cuba there are very large deposits of these Mayari type iron ores. They have high iron contents and therefore should be very valuable as a source of iron in the manufacture of iron and steel. As yet, however, these ores have not been utilized except for certain limited purposes because of the fact that heretofore there has been no effective and economical method devised for the removal of nickel therefrom. Other substances beside nickel are present in Mayari ores which should be removed to render the ores fully effective for use in the manufacture of iron and steel, such as chromium, aluminum, and cobalt. The primary difiiculty, however, is that of removing nickel. These ores contain nickel in such an amount and in such a condition as have heretofore prevented them being commercially beneficiated for use in the general manufacture of iron and steel. This difiiculty in lowering nickel to the necessary extent is primarily due to the fact that a substantial part of the nickel is in such a state or is so bound to or combined with the other constitcents of the ore as not to-be easily removed from the ore to bring the nickel content down to a sufiiciently low figure.

Among the best known Mayari type iron ores are the so-called Mayari ores. Mayari ores as they occnr'in nature contain considerable free water and also a substantial amount of combined water. Analyses of the calcined ores vary considerably but in. general they run within ranges approximately as follows:

Percent Percent 1. 0 0.25 to 1.56. 2.2 20 to 2.7. 0.15 0.05 to 0.35. 0.5 0.24 to 1.76. 5.0 1.6 to 7.0. 10. 0 6.0 to 14 0 In this table of analyses, the first column indicates the constituents of the ore; the second column indicates an average analysis; and the remainder of the tableindicates the ranges. When, in this specification, I refer to Mayari type ores I mean those ores which, like the Mayari ores, have a considerable content of iron and contain nickel in a substantially lesser amount but still in an amount too great for general iron and steel making, and in which ores the nickel is difficult to reduce to the necessarilysmall amounts required for general iron and steel making.

My invention comprises the steps of mixing'the material containing nickel and iron or nickel, cobalt and iron with an aqueous solution of nitric acid,subjecting compounds of such mixture to high temperatures and pressures in an autoclave to produce an aqueous solution of nickel nitrate or nickel and cobalt nitrates and obtaining iron in the solid phase, and separating the solution from the iron.

Myinvention is based, in part, on my discovery that ferric nitrate in unstable in aqueous solution under certain conditions and forms nitric acid and ferric oxide, which latter is insoluble and is precipitated, whereas nickel nitrate and cobalt nitrate in aqueous solution and under the same conditions are essentially stable and remain in solution. The conditions which produce this difference of stability of ferric and nickel nitrates may be indicated as follows. When an aqueous solution of ferric nitrate and free nitric acid is autoclaved at certain high temperatures the ferric nitrate forms nitric acid, which remains in solution, and ferric oxide which is precipitated. When an aqueous solution of nickel nitrate and free nitric acid is autoclaved at the same temperatures the nickel nitrate is unaffected and remains in solution. The discovery of the fact that there are temperatures at which ferric nitrate in aqueous solution containing free nitric acid is unstable but at which temperatures nickel nitrate under the sameconditions is stable has two significant aspects as regards my invention. Where in this disclosure I refer to ferric oxide being formed and precipitated I desire the expression ferric oxide to cover not only ferric oxide itself but hydrated ferric oxide or ferric hydroxide as under varying conditions of operation either of these compounds may be formed.

One aspect of this discovery is the fact that when an aqueous solution containing free nitric acid and ferric and nickel nitrates is heated in an autoclave to temperatures where the ferric nitrate is unstable out the nickel nitrate is stable there results the precipitation of ferric oxide but the nickel nitrate remains in' solution thereby permitting the separation of iron and nickel by removing the nickel nitrate solution from the precipitated iron product. An-

other aspect is the fact that when a material containing nickel and iron isheatedinan autoclavewith an aqueous solution of nitric acid to-- those temperatures -where ferric nitrate is unstable but where nickel "nitrate is stable the nickel of the material forms nickelnitrate and goes into that the iron may ferricnitrate because; of its instability solution, while the major-part of the iron-is'undissolved. Of course, there isthetheoretical possibility inthis'case first form ferric 'nitratebut, if so, the

under the conditions forms ferric-oxide and nitric acid and therefore, in effect at least, it is as if the iron'in thematerial were unaflected by thenitric acid. v l My invention comprises two} main "for separating nickel from iron, spending to the two aspects of modes of procedure these two modes corremy discovery outlined above. In' one'bf'these modes of procedure the material containing nickel and iron is subjected to the action of "an aqueoussolution"of nitric acid to dissolve the major part' ofboth for a sufficient time the nickel and iron as nickel and ferric nitrates. If the material being treated contains constituents of ble nitrates, these elements will-also go into solution. A

other elements which form soluform nitrateswhich 'quantity of'nitric acidsolution will be employed sufiicient'to'provide contained nitric acid *to nitratethe ma'jor part of the iron, nickel, and other -nitrate for'mingconstituents. 1 The solutioncontaining --thenitrate isseparated from .the' undissolved residue and autdclaved at a temperature at which the ferric nitrate is unstable but at which-" temperature nickel "nitrate is -'s\'1bstantiallystable. {ferric nitrate in solution nitric acid" formed the' latter being precipitated.

":As 'resultof' this treatmentof the and 1 ferric oxide are The nickel nitrate,

being stable under; the 'conditionsigiven, is unafiected and remains in: solutionas.- nickel "nitrate. taining nitric acid andnickel nitrate is -from the iron bearing residue. venience "I shall hereafter referto The solution conthen separated For purposes of conthismode of procedure as--the N1= -process. The claims of the present application 'aredirected to "this N-l process.

In the ZSCCOnd main mode of procedure,

containing the material nickel :and iron is mixed with anaqueous solution of nitric acid, the amount of solution employed beingsuch' thatthe contained .nitric acid is at' least suf- -fieient-to meet the-stoichiometricrequirements of -the 'ni'ckel-andother non-fer rous nitrate i of-=the material-in theirs-conversionforming constituents into nitratesbut insuflicient" to meet such requirements andalso to nitrate amajorportion ofthe iron-in the material.

The mixture isthenautoclaved at a temperature at which ferric nitrate is unstable but at=which-nickel-nitrate is essentially stable. Under-these conditions the .nickel is dissolved as nickel nitrate. The 'major partof' the :iron-,- however, remains undisolvedinthe materialibeing treated: Following the autoclaving operation-the solution containing nickel nitrate" is separated-from the iron bearingresidue.

purposes of convenience I as the 'N2 process. "process" are contained in rny apphca For refer-to this mode of procedure Glai-ms' directed tothis -N-2 tion' Serial- No.- 274,-

'055, filed February 28,1952; referred to above.

I'shall now givea specific-description of anembodiment of-the first of; the two-modes of have designated above ascific example, Mayariore is procedure, namely what I the N-"l process.v

In this spefirst dried. It isthen ground 65 mesh. Mostof this-Mayari ore isfinerathan 65 but the grinding. operationreducesthe coarser parts of the ore to a'suflicient fineness The ore is then roasted in for further treatment. air at about 800 F. My process iseffective withoutthistype ofroast but I prefer to I employ it as it removes mostof the waterremai-ning in the ore and it improves the-subsequent extraction of iron from the ore and improves the washing characteristics. of

- the ore during subsequent treatment.

' :The ore isthen mixed with a solution of nitric acid of 25% concentration at 200 F. to dissolve the major part of the iron, nickel and cobalt. The quantity of acid used is such as to be somewhat in excess of the amount which theoretically would dissolve all the iron, nickel,

5 cobalt, manganese and aluminum and part of the chromium in the ore.

The solution thus produced is separated from the undissolved residueand pumped into an autoclave which is heated with saturated steam, 400 p. s. i. gage, which is fed directly into an autoclave to heat the contentsto a temperature of 400- F. In this specific examplev of my process the autoclaving operation is continuous, i., e. the solution is fed continuously into alower part of the autoclave and discharged continuously from an upper part of the autoclave. The rate of .flow oflsolution into the autoclave and the rate of discharge therefrom are such that the average detention time of material in the autoclave is 68-minutesin this specific: example. Theronbtents'of the autoclave are continuously -agitated during its operation. This treatment in the autoclave. :effects the precipitation of .thecmajor part of the iron in, the

, solution. and also about half of the chromium v of .the

- solution as oxides. The solution contains most of the nickel as well .as other: non-ferrous. materials. as. well as 1 some free .nitric acid. Thesolution and precipitated .product are separated,. and the precipitated product thoroughly washed. Thesolution, after its separation from the autoclave, is evaporated-somewhat and about three-fourths ofitmixed with free nitric acidsolution and used for .the treatment of more ore, and about onefourth of the solution is pumped to the acid ,and .byproduct :recoveryplantwhere the nickeland other valuableconstituents ..may be :recovered inany ,suitable manner.

.Thezprecipitated iron bearing product .is very lowin .nickel,.the amount present being-about 0.01%. -A sample of-the material after .beingcalcined, will analyze. substantially as follows:

. In; the justomentioned: example ofwmyvinvention; .the '.conditions: areasetforth specifically. :Thevariouscondiutionsmay vary over considerable ranges:and yet:.come

%-within :the scopen ofamyi ainvention. In 1 dissolving the major: =part:of:. the :iron, nickel, manganese; aluminum: and cobalt-a and part ofithepchromium in.-the ore'prior to autoclaving, itheaconcentration ofunitric acidisanot critical.

Thesconcentrations mayavary from. 10% to 70% although I prefer a. concentration of not -over.6 0%. Theamount r-of acid: used:may vary considerably .but .I prefentomse :somewhat inexcess of .the amount oi acid'awhich theoreti- ..cally would be-required to combine-with all-;.the iron, nickel, cobalt,-rnanganeseand aluminum in the. ore. The

temperature of the acid when being used: to1dissolve; the *iron; nickel andrcobalt is not, critical. .qPreferably, it is at. least 100 Fraud may 'be as high as theboiling point. :point.

:..-:The-temperature: of autoclaving may ;vary from-.365

Fato 650 F. For themostrapid;precipitation'zofiron it is desirable to-employ temperatures from-385? E.:.and v. up. :Moreover,--theuhigher-temperatures increase th yield ofiron, otherconditions being the; same; .ThGE-fill'lfi -foriautoclavinga 4 may vary considerably .althoughi'ithe Io-longer. periods ofltime. .tend to, give ,a more,icomplete precipitation of iron.

ln the specific example given above, the autoclaving treatment is -continu0us.- While Iprefenthecontinuous method-for manipulativeiand economic reasons my proc- .ess is fullyzefiectiveschemically when a batch, method is employed. By the batch method I mean that method of procedure whereby the autoclave is charged with a material to be treated, autoclaved and then discharged, following which another batch may be charged and treated, and so on. In general I find that the batch method requires a somewhat lesser time of stay in the autoclave than the average detention time required in the continuous method to give the same results.

In the specific example given above of the N-l process the analysis of the iron product obtained shows a chromium content of 1.0%. This content is somewhat higher than is desired in iron bearing material for making many kinds of steels. The N-l process may advantageously be combined with treatment for removing chromium. An example for producing an iron product low in nickel, cobalt and chromium follows.

Mayari ore is mixed with soda ash, using 80 parts of soda ash per 100 parts of contained calcined ore. This mixture is roasted at a temperature of from 1700 F. to 1900 F. for one hour. The roasted product is then treated with water to remove the soluble parts thereof. The roasting of the Mayari ore and the subsequent extraction of soluble matter by means of water reduces the content of the chromium to a very low figure; in this specific example the chromium content is reduced to less than 0.10%. This treatment also removes most of the alumina.

The treated product, low in alumina and chromium but still containing practically all of the nickel and cobalt of the original ore is now subjected to the N-1 process to obtain an iron containing product in which the nickel and cobalt is reduced to the desired degree. In practice it will be found that in the N-l process less acid may be used than when ores are treated which have not been subjected to the chromium removing treatment. This is because of the fact that the removal of most of the alumina gives a product having considerably less material which can react with nitric acid to form soluble nitrates. In the specific example of treatment to remove chromium, given above, the reagent employed in the roasting step is soda ash (NazCOa). Other substances are equivalents for the purpose of removing chromium. Any alkali may be used such as the carbonate, bicarbonate, hydroxide of sodium or potassium or mixtures of combinations of these compounds.

The amount of alkali to use should be at least such that the reagent is stoichiometrically equivalent to the aluminum and chromium contained in the ore. In practice I prefer to use in excess of this amount. In the specific example given above the amount employed is considerably in excess of the stoichiometric requirements of the aluminum and chromium.

I have found that the use of the roast with alkali followed by the subsequent removal of soluble matter by means of water not only greatly reduces the content of chromium but it also changes the nature of the ore in such a way that it is more readily acted upon by nitric acid in the N-l process.

I claim:

1. A process of treating iron ore containing nickel, comprising the steps of mixing the material with an aqueous solution of nitric acid in an amount at least suflicient to combine with the major portion of the iron and also combine with the non-ferrous constituents of the material capable of being dissolved by nitric acid, maintaining the acid and material in contact a sufiicient period of time to dissolve the major portion of the iron and nickel of the material, separating the solution from the undissolved portion of the material, and autoclaving the solution at a temperature between 365 F. and 650 F. to obtain a solid phase containing iron and a solution containing the major portion of the nickel of the material.

2. A process of treating Mayari type iron ore containing nickel to produce an iron bearing product low in nickel and cobalt, comprising the steps of treating the ore with an aqueous solution of nitric acid of from 10% to concentration, in amount at least sufficient to satisfy th stoichiometric requirements of the major part of the iron, nickel and other nitrate forming constituents of the ore, for a sufiicient time to dissolve the major part of the iron, nickel and cobalt, separating the solution from the undissolved residue, subjecting the solution to autoclaving at a temperature of from 365 F. to 650 F. for a sufiicient time to precipitate most of the iron, and separating the solution containing most of the nickel and cobalt from the precipitated product.

3. A process of treating Mayari type ore containing nickel to produce an iron bearing product low in nickel, comprising the steps of treating the ore with an aqueous solution of nitric acid of from 10% to 70% concentration, in amount at least suificient to satisfy the stoichiometric requirements of the major part of the iron, nickel and other nitrate forming constituents of the ore, for a sufficient time to dissolve the major part of the iron, nickel and cobalt, separating the solution from the undissolved residue, subjecting the solution to autoclaving at a temperature of from 385 F. to 550 F. for a sulficient time to precipitate most of the dissolved iron, and separating the solution containing most of the nickel and cobalt from the precipitated product.

4. A process for treating Mayari type iron ore containing nickel to produce a product low in nickel, cobalt and chromium, comprising the steps of roasting the ore with alkali under oxidizing conditions, dissolving the soluble constituents with water and removing the solution from the roasted product, treating the product with an aqueous solution of nitric acid of from 10% to 70% concentration, in amount at least sufiicient to satisfy the stoichiometric requirements of the major part of the iron, nickel and other nitrate forming constituents of the ore, for a suflicient time to dissolve the major part of the iron, nickel and cobalt, separating the solution from the undissolved residue, and subjecting the solution to autoclaving at a temperature of from 365 F. to 650 F. for a suificient time to precipitate iron, and separating the solution containing nickel and cobalt from the precipitated product.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Report of Investigations 3626, March 1942. Manganese Investigations. Published by Bureau of Mines, Washington, D. C. Entire report is relied upon and has 30 pages and 7 figures. Pages 4, 5, 6, 7, 10, 11, 15, 24 and 26 pertinent. 

1. A PROCESS OF TREATING IRON ORE CONTAINING NICKEL, COMPRISING THE STEPS OF MIXING THE MATERIAL WITH AN AQUEOUS SOLUTION OF NITRIC ACID IN AN AMOUNT AT LEAST SUFFICIENT TO COMBINE WITH THE MAJOR PORTION OF THE IRON AND ALSO COMBINE WITH THE NON-FERROUS CONSTITUENTS OF THE MATERIAL CAPABLE OF BEING DISSOLVED BY NITRIC ACID, MAINTAINING THE ACID AND MATERIAL IN CONTACT A SUFFICIENT PERIOD OF TIME TO DISSOLVE THE MAJOR PORTION OF THE IRON AND NICKEL OF THE MATERIAL, SEPARATING THE SOLUTION FROM THE UNDISSOLVED PORTION OF THE MATERIAL, AND AUTOCLAVING THE SOLUTION AT A TEMPERATURE BETWEEN 365* F. AND 650* F. TO OBTAIN A SOLID PHASE CONTAINING IRON AND A SOLUTION CONTAINING THE MAJOR PORTION OF THE NICKEL OF THE MATERIAL. 